xring.......why does increased battery voltage when running surprize you??? How do you think batterys gitt charged??? 1-wire ...or... 3-wire ALL the same. Connect yer voltmeter between Ignition switch ON and ground. Iff'n meter read WRONG polarity, just swap the meter leads. Simple, eh?
The reason you want to connect to ignition switch ON is the voltmeter can "drain" yer battery in about 1-weeks time. Then you'll be complaining again about dead battery. When used daily, the alternator/generator re-charges the battery. The original "loop" ammeter does NOT drain yer battery, nether does the 2-terminal ammeter. ........Dell, yer self-appointed sparkie-meister